A multiport amplifier is provided with an input hybrid, an output hybrid, and a plurality of amplifiers connected between them, wherein input signals having different frequency components are inputted to a plurality of input terminals of the input hybrid, and are distributed, amplified and combined, and output signals having frequency components different from those of the above-mentioned input signals are outputted from a plurality of output terminals of the output hybrid. As a result of this, the individual amplifiers are of an arrangement to amplify all the different frequency components, and hence, it is possible to decrease the deterioration of communication quality at the time of the failure of the amplifiers, as compared with an arrangement in which an amplifier is provided for each of the frequency components.
Conventionally, there has been proposed a hybrid matrix amplification system (multiport amplifier) which serves to compensate for a gain error and a phase error (for example, see a first patent document).
FIG. 15 and FIG. 16 are circuit block diagrams showing a multiport amplifier which is described in the first patent document.
In FIG. 15, signals that have been extracted by couplers 355 through 358 are combined into a composite signal by means of a combiner 390, and in FIG. 16, signals that have been extracted by couplers 381 through 384 are combined into a composite signal by means of a combiner 396. As a result of this, in a feedback circuit 303, control signals for compensating for the gain error and the phase error of the amplifiers 350 through 353 or the amplifiers 375 through 378 are obtained based on the composite signals.
However, if the multiport amplifier is constructed as shown in FIG. 15 and FIG. 16, there will be a possibility that a signal of a small amplitude can not be received with a high degree of accuracy due to the limitation of the dynamic range of the reception sensitivity of circuits (RF reception units 391, 397) which receive the composite signals.